Organic pigments are, in general, obtained from their synthesis in a physical state which is unsuitable for use. These crude pigments have, for example, a coarse particle size, a non-uniform or unsuitable crystal shape, or an excessive aggregation tendency. Crude pigments are therefore comminuted, and the residues of starting materials, undesirable by-products and the like are removed. The powders as obtained, however, have poor coloristic properties on account of a broad particle-sized spectrum.
Phthalocyanine pigment has been used as a color source in many industries including inks, coatings, plastics and textiles. In many cases, the desired shade or hue of the phthalocyanine pigment is that of the green (.beta. crystal) shade. As synthesized crude phthalocyanine of the .beta. form is blue, but, due to its large particle size, poor color strength and an inherent dirty red shade, it is typically processed further to the more desired green shade via milling, or grinding, with salts and solvents.
Specially designed additives, such as grinding aids and/or dispersants are required for direct conversion of phthalocyanine blue pigment by media milling because the conversion includes not only the breaking of agglomerates to their primary particle size but also goes one step further. The phthalocyanine blue crude starts as a red shade crystal, but the milling breaks the crystal structure into the unstable "Y" .alpha. crystal and causes a lattice change to produce the green shade .beta. crystal. A milling process (media size=0.25 mm) which induces a high amount of work and energy into the pigment dispersion is required to facilitate pigment crystal fracture, lattice structure shift and ultimately, pigment conversion. In addition to providing the properties of pigment wetting and stabilization, these additives also need to provide the grinding medium and composition with the proper rheology, viscosity and temperature stability due to the high energy nature of the process.
The salt grind process utilizes sodium chloride and glycols such ethylene glycol, diethylene glycol, or triethylene glycol, to break down the agglomerates and finally change crystal structure of .beta. crude to the .alpha. form. The .alpha. crystal, however, is a red shade and it must be further reduced in particle size to the more thermodynamically stable .beta. crystal via long grind times and high temperatures of &gt;100.degree. C. The "salt grind" process for conversion of crude phthalocyanine blue typically takes up to 24 hours and produces copious amounts of excess solvent and wastewater.
Thus, the traditional conversion of crude phthalocyanine blue by the salt grind process has the following drawbacks:
______________________________________ environmental concerns from wastewater created by the washing of salts and solvents long processing times of up to 24 hr many processing steps-once conversion is complete, it must be reprocessed into a sellable/usable form such as finished pigment dispersion ______________________________________
U.S. Pat. No. 2,816,115 discloses converting a crude phthalocyanine coloring matter in .beta. form to a pigmentary state without converting the coloring matter into the .alpha. form by milling it in an aqueous environment comprising a comminuted water-insoluble, solid grinding agent and a water soluble dispersing agent containing an anionic, water-soluble compound having relatively strong dispersing powers.
U.S. Pat. No. 3,593,927 discloses a process of comminution of an aqueous suspension of .beta. copper phthalocyanine, by vigorous agitation in a grinding mill, with a particulate grinding aid, in the presence of an alkyl glycol ether having at least one ethylene glycol unit in the molecule and of one or more amine salts bearing at least one alkyl substituent having 12 or more carbon atoms in the chain.
U.S. Pat. No. 4,158,572 discloses a process for producing a phthalocyanine pigment comprising dry grinding a crude phthalocyanine, stirring the ground product with an aqueous medium containing a nonionic surfactant and isolating the pigmentary product, the preferred nonionic surfactant being ethoxylated alkyl phenols.
U.S. Pat. No. 4,427,810 discloses a method for producing an aqueous dispersion of phthalocyanine blue pigment comprising mixing in water a phthalocyanine crude pigment with a surfactant and grinding the mixture. Useful surfactants have an HLB value greater than 8 and include water-soluble, nonionic, cationic and anionic types.
GB 2,039,290 discloses converting crude copper phthalocyanine into an easily dispersible deeply colored pigmentary form without the use of organic solvents by dry milling the crude pigment in the absence of chemical milling assistants until the milled material consists of agglomerates which are composed of primary particles of &lt;0.1 .mu.m in size, followed by admixing the milled material with water and heating the mixture in the presence of at least 3 wt % surfactant but in the absence of shear forces effective to comminute the primary pigment particles, thereby recrystallizing the pigment, and isolating the recrystallized pigment. The milled material which is mixed with water is obtained by milling a mixture of crude copper phthalocyanine and 0.5 to 15 wt % acid which has a pK of &lt;4.9 and is non-oxidizing under the milling conditions.
U.S. Pat. No. 5,852,179 discloses the use of alkoxylated acetylenic diol surfactants in aqueous synthesis of dispersed azo dyes to provide a simple process for improving the filtration properties of dyestuff. The surfactants may be added prior to the coupling steps of the synthesis or prior to heat treatment of the dye slurry. For azo dyes that are synthesized as non-heat-stable crystal modifications, the presence of alkoxylated acetylenic diol surfactants in the dye slurry is effective in promoting the conversion of the dye to the desired thermally stable crystal modification.